Using attachMovie multiple times to create a tile background

I'm want to tile a 700 x 700 area using attachMovie().

The movieclips used for the attachMovie is 50 x 50

This is the code. Something is wrong here.

var NuX:Number=0;

var NuY:Number=0;

var btnX:Array=[gpat_btn0, gpat_btn1, gpat_btn2];

var attX:Array=["pat0","pat1","pat2"];

for(i=0;i<btnX.length;i++){

  btnX.pvar=i;

  btnX.onRelease = function(){

  NuX=NuY=0;

  for(j=0;j<14;j++){

  if(NuX>=650){

  NuX=0;

  NuY=NuY+50;

  }

  _root.movieC1.movieC2.clip0.attachMovie(attX[this.pvar], attX[this.pvar]+j, _root.movieC1.movieC2.getNextHighestDepth(), {_x:NuX, _y:NuY});

  NuX=NuX+50;

  //trace(NuX)

  }

  }

}